In wireless communication systems, multiple input multiple output (MIMO), is an antenna technique configured to improve the spectral efficiency and thereby boost overall system capacity. The MIMO technique uses a commonly known notation (M×N) to represent MIMO configuration in terms number of transmit (M) and receive antennas (N) on one end of the transmission system. MIMO systems can significantly increase the data carrying capacity of wireless systems. MIMO can be used for achieving diversity gain, spatial multiplexing gain and beamforming gain.
In new radio, sometimes referred to as 5G, user equipment computes channel estimates based on pilot or reference signals from the 5G system, and computes the parameters needed for channel state information (CSI) reporting. A CSI report, including channel quality indicator (CQI) data, is sent from the user equipment to a network device on demand via a feedback channel on request from the network, and/or the user equipment may be configured to send the CSI report periodically. A network scheduler uses this information in choosing the parameters for scheduling of this particular user equipment. The network sends the scheduling parameters to the user equipment in a downlink control channel. After that, actual data transfer takes place from the network to the user equipment.
While MIMO provides many benefits, in new radio, the performance of conventional MIMO systems degrades under certain conditions, including at high user equipment speeds. More particularly, when a mobile device is moving at high speeds, the receiver of a signal is moving in relation to the transmitter, resulting in the Doppler effect because the frequency of the signal is shifted, such that it is perceived to be different at the receiver than at the transmitter. The performance degradation is severe when the signal to noise ratio (SNR) is high. If the rank in transmission is high, it is also the case that the SNR is high. For high rank systems, the impact due to mismatch between the transmitter and receiver channel qualities is severe.